I am sorta new to flyfishing streams. I might not know everything about stream fishing, but I know how to get a few fish every time I'm out. Here are some of the things I do to get on the fish.
I always knew that you needed to find what the trout are feeding on. So when ever I get to a stream I look for any bugs on the water, flying around, or swimming. I take my net and swipe up a couple bugs. I look at them and look at my fly boxes. I tie on the closest immitation I have of the insect and start fishing. If that doesn't work, I try other fly, usually a patch adams.
If you can see any thing rising and then flying away use an emerger. I think that when they are tied on a curved shank they look way better than on a standard straight shank. Even unweighted nymphs will sit neutral and give the appearance of an emerging bug.
If there are no trout coming up to the top, I grab a few rocks about softball size and look at the bottoms of them. If they have any thing on them, I put the fly that looks like that on. Sometimes you can even see some scud shoot out from where the rocks were --scuds will work at times--.
When you use any fly, make sure you fish it just like the real thing. I really think that this might be one of the most important rules in catching trout on the fly. If it helps, purchase a fly chart from your local fly shop and look it over before you head out. One great advantage is tying your own flies. You can't go to the pro shop and get any thing you want. They simply can't make that many different flies. Some even prefer to bring the vise to the stream, in case, they don't have the right fly. Fly charts will give you a heads up of what flies you will need to prepare your self with.
One rule my flyfishing partner is always enforcing is "stay away from the bank." I know that the trout can see you, but if you stay there long enough, they won't notice you and you can still get a few trout. When ever we go fishing we always accomplish 3 things: lots of fun, good snap shots, and a hand full of nice trout.
Good luck and tight lines